Automobiles, especially passenger cars, are often provided with a security alarm system which, when not properly de-activated, generates an alarm signal when the car door is opened by an un-authorized person in an un-authorized manner. Besides the function of activation/deactivation of the system, most of the car security alarm systems have additional functions, such as car searching which flashes the car lights so that the car driver may easily locate the car, especially in a dark environment. To provide a communication between the car driver and the car, the car security alarm system comprises a transmitter portion which is usually made portable or hand-holdable so as to be carried and operated by the car driver when the car driver is out of the car and a receiver portion which is incorporated in the car electrical system and powered thereby. The receiver portion is in electrical connection with the car lights for selectively turning on the car lights to flash and mechanically coupled to the car door locking mechanism for locking/unlocking the car door upon receiving instruction from the transmitter portion.
The transmitter is usually provided with several push buttons respectively associated with different functions, such as alarm system activation/de-activation and car searching. In operation, the car driver has to actuate the desired one of the push buttons to activate the desired function of the car security alarm system. In actuating the push button, the transmitter portion which comprises a circuit therein emits a signal associated with the selected function to the receiver portion which, upon receiving and identifying the signal, activates the associated function. This, although providing an effective communication between the car and car driver, yet- is to some extent inconvenient. For example, when the car driver approaches the car and wishes to de-activate the security alarm system and thus unlock the car door, the car driver has to pick up the transmitter and push the button associated with the system deactivation function. The conventional system is not capable of identifying the approach of the car driver and will not automatically unlock the car door.
In addition, some of the car drivers who may be very absent-minded, may forget to activate the car security alarm or even forget to lock the car door when he or she gets out and leaves the car. This exposes the car to the danger of un-authorized use or break-in.
Thus, it particularly needs to improve the car security alarm system to incorporate the function of automatically locking/unlocking car door when the car driver leaves/approaches the car so as to overcome the drawbacks of the conventional system.